Continuously recorded electrocardiograms and direct blood pressure measurements will be used to characterize the cardiovascular response of coronary patients to a variety of laboratory conditions: dynamic and static work, alone and in combination; psychological stress; eating; smoking; and cold. These responses will be used to document the stability of the "threshold" of heart rate and blood pressure at which ischemic ST-segment depression and angina occur. Ambulatory electrocardiograms recorded under the conditions noted above will be subjected to a computerized ST-segment analysis program. Documentation of accompaniments of "ischemic" ST-segment responses will help to determine whether myocardial ischemia is acutally present. Ambulatory electrocardiography on the job will be compared to ECG recordings made in the laboratory, in order to document the utility of the laboratory assessment. If readily available laboratory methods as treadmill exercise testing performed at 3 or 4 weeks following infarction may detect most ischemic abnormalities and ventricular ectopic activity noted by more elaborate methods, such as ambulatory electrocardiography, occupational work assessment will be considerably simplified. Prospective clinical trials of earlier return to work following infarction would then be ethically justifiable.